FV 25 Interhemispheric connectivity of frontoparietal motor regions aids grasping performance after stroke

Abstract

Introduction: After a stroke, increased neural activation in the contralesional primary motor cortex (M1) and the anterior intraparietal sulcus (aIPS) has been discussed to indicate supporting or disturbing roles for motor function, depending on patients‘ impairment and motor network connectivity (Di Pino et al., 2014). Prior studies have focused on interfering with M1 during the execution of simple motor tasks to test this hypothesis using online-rTMS. However, parietal areas are typically engaged in more demanding tasks. We hence combined task and resting-state fMRI, followed by neuronavigated online-rTMS to assess the roles of M1 and aIPS for complex upper limb movements in relation to interhemispheric resting-state functional connectivity (RSFC) with their ipsilesional counterparts. Methods: Resting fMRI and task fMRI were acquired from 18 chronic stroke patients and 18 age-matched controls. Task-related activation peaks in bilateral aIPS as well as the electrophysiological hotspot in contralesional M1 were identified in each participant and targeted by online-rTMS (10 Hz trains, 90% of resting motor threshold) during (i) index finger-tapping, (ii) reach-to-point, and (iii) reach-to-grasp movements. For sham rTMS, the coil was tilted over the parieto-occipital vertex. We analyzed 3D hand kinematics (smoothness, efficiency, accuracy, speed) in each task and clustered well and poorly recovered patients using K means. Additionally, we extracted performance across all kinematic data by multiple factor analysis. Kinematics during real online rTMS were normalized to the sham condition and correlated with RSFC between bilateral M1, aIPS, and dorsal premotor cortex (dPMC; Rehme et al., 2012). Results: Clustering of kinematics yielded one cluster with healthy controls and recovered patients as opposed to a second cluster with impaired patients. RSFC between bilateral aIPS and between ipsilesional aIPS and dorsal premotor cortex was higher in recovered compared to impaired patients. Interhemispheric connectivity between bilateral M1 and ipsilesional aIPS with contralesional M1 correlated with better motor performance. Online rTMS revealed that patients with increased RSFC between bilateral M1 were impaired in grasping speed when interfering with contralesional M1, whereas patients with increased RSFC between bilateral aIPS deteriorated in grasping accuracy when interfering with contralesional aIPS. Conclusion: The present findings suggest a link between stroke impairment and interhemispheric RSFC between bilateral M1 and aIPS. Interfering with contralesional M1 and aIPS further showed a supportive role of M1 and aIPS in patients with higher interhemispheric connectivity. This finding may indicate that resources from the contralesional M1 and aIPS are accessed via transcallosal connections, aiding different aspects of complex hand movements in chronic stroke. References Di Pino G et al. Nat Rev Neurol 2014. Rehme AK et al. NeuroImage 2012.